How might the DDR have developed if somewhat less land had been given to Poland after the war (for instance, Stettin and other parts of Silesia and Pomerania) [...]?
That'd make virtually no difference as it doesn't change the structure of the system. The Problem of the GDR wasn't the number of displaced Person, nor enough farmland (it could basically feed its population with homemade-food such as bread and potatoes), nor enough industry (rather more how much of it the Soviets took away after 1945 and how difficult it was to replace these losses wheras Western companies took up credits and modernizes what they had to pay as reparations, actually giving them a competitive edge), and not even the lack of a big harbour such as Stettin (as they wouldn't make proper use of it).
Overall: the mismanagement and political oppression coming with the Stalinist System would not change. So, 1953 would probably still happen, just also east of the Oder and Neisse. Ulbricht would still feel forced to build the Berlin Wall and so on.
This was exacerbated by the existence and success of the FRG on the basis of a shared culture, language and pre-war economic history. Unlike Hungarians or Polish, the GDR population always had at arm's length a look at "what a German economy can accomplish".
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Concerning the "tribal" Situation of the GDR - the main issue IMHO was that it lumped together two mentalities which didn't fit well. Prussians and Saxons were traditional rivals and see themselves as having a somewhat different mentality. Saxons could view the GDR with its militarism and rigidity negatively as Prussian; whereas non-Saxons listened to Ulbricht's distinct Saxon dialect and view the GDR negatively as Saxon.
[see: https://en.wikipedia.org/wiki/Upper_Saxon_German]